In recent years, efforts have been made to develop instruments and procedures for use in minimally invasive hip arthroplasty procedures. In minimally invasive surgical (“MIS”) procedures, the operation is carried out through a small incision, such as an 8 cm incision. MIS procedures may reduce trauma to the patient's muscles and other tissues, and typically result in shorter patient recovery time. However, operating in the confines of a small incision presents challenges to the surgeon. The surgeon must often rely on specialized surgical instruments in order to access or operate within the surgical site.
In addition to MIS procedures, efforts have been made to develop bone conserving hip arthroplasty procedures. In conventional total hip arthroplasty, the head and neck of the natural femur are removed and replaced with an artificial femoral head and neck. The artificial head and neck are attached to a stem that is secured in the intramedullary canal of the femur. Over the years, total hip arthroplasty has had excellent clinical success. However, various conditions can arise in which it becomes necessary to perform revision surgery on the hip joint. The presence of the implant in the femur can sometimes result in stress shielding, osteolysis or other conditions that lead to the gradual loss of bone stock and loosening of the implant. An infection may require removal of the implant. Additionally, the useful life of an artificial hip joint is about 15 to 25 years, and a young hip patient will therefore typically require a revision surgery at some point in his or her lifetime.
When performing a revision hip procedure, it is desirable to have as much bone stock available as possible. Accordingly, efforts have been made to develop surface replacement arthroplasty procedures that preserve bone stock in hip procedures. In surface replacement arthroplasty of the hip, the natural femoral head and neck are preserved, but are resurfaced to receive an artificial femoral head. An example of such a femoral head for use in surface replacement arthroplasty procedures is shown in FIGS. 1, 2, 7 and 8 of U.S. Pat. No. 6,156,069 (Amstutz), which is incorporated herein by reference. As shown in FIG. 1 of Amstutz, the femoral head includes a central tapered stem and a spherical surface replacement portion. An inner surface of the prosthesis covers the reamed bone of the femoral head, while the central tapered stem is centered in the femoral head and neck. Femoral heads of the type shown in Amstutz are available from applicant, Wright Medical Technology, Inc. 5677 Airline Road, Arlington, Tenn. 38002.
Instruments have been designed for measuring a patient's femoral head. U.S. Pat. No. 4,517,969, (Halcomb, III et al.) discloses a prosthetic gauge which is used for evaluating the fit of a prosthetic device against a receiving bone or cartilage surface. The gauge includes a portion for gripping and a contact portion extending from the gripping portion. The surface of the contact portion is predeterminedly contoured to conform substantially to the shape of the receiving bone or cartilage surface to be evaluated. The contact surface is a frosted or translucent surface which transmits and diffuses light so that the specific bone or cartilage surface being observed through the gauge cannot be seen clearly until actual contact is made between the contact surface and the articular surface. This aids the surgeon in more accurately determining the apparent contact area, and hence in evaluating the potential fit of the prosthesis. The Holcomb gauge is described primarily with reference to an acetabular gauge, but the patent mentions that the principles can be applied to any suitable prosthetic gauge, and notes that a concave hemispherical, translucent contact surface could be used to measure the femoral head size.
U.S. Pat. No. 5,070,623 (Barnes) discloses a manually operated gauge for the simultaneous measurement of two orthogonal diameters of a spherical member. The gauge comprises four shaped bars all pivotably connected together about four parallel pivot axes, the bars arranged to enclose a measurement or work space into which the spherical member to be measured may be brought. Two main arms are pivotably joined at one end and each is provided with a pair of orthogonally oriented contact surfaces at the other end, the contact surfaces adapted to arcuately move with their respective arms about the arm-pivot in order to capture a spherical member between them. A scale member is pivotably connected to the free end of one of the arms and an indicator member is pivotably joined to the free end of the other of the arms. The scale member and the indicator member are pivotably connected to each other about an axis aligned along the center line of the gauge while the other ends of the scale member and the indicator member cooperate to indicate the size of the spherical component being measured.
The background section of Barnes, at Col. 1, Lines 41-60, states that instruments for measuring the diameter of spherical prosthetic heads include open-faced templates and contour gauges provided in a range of discrete sizes so that the surgeon must select the gauge closest in size to the actual head being measured. Barnes further notes that some spherical head gauges are available as a set of discretely sized, closed circular openings which are used by matching the head being measured to the circular opening having the best fit. Barnes states that these types of gauges are analogous to the aforementioned contour gauges, but that the contour gauge only provides an arcuate portion of a particular circular opening while the circular gauge provides the entire circular opening.
US 2004/10193175 A1 (Maroney) discloses a femoral gauge for measuring the contour of the femur for use in hip arthroplasty (see particularly FIG. 25). The gauge includes a body and a probe. The body has a body contact portion of the body for contact with the femur. The probe is movably positional with respect to the body. The probe includes a contact portion of the probe for contact with the femur. The relative position of the probe with respect to the body is indicative of the femur contour of the femur.